It is known that ammonium salts of aromatic carboxylic acids can be prepared by introducing gaseous ammonia into a solution of an aromatic carboxylic acid in an aprotic solvent. DE 1115729 describes such a process which employs dimethylformamide as solvent. U.S. Pat. No. 2,220,692 describes a process for preparing ammonium mandelate which involves treating a dispersion of mandelic acid in anhydrous benzene with ammonia. DE 2005514 describes a process for preparing thiolsulfinates by oxidizing the episulfides using an organic peracid, in particular perbenzoic acid, and precipitating the by-produced acid by introducing dry ammonia as the ammonium salt. The precipitation requires a low temperature of from −50 to −30° C.
Zh. Prikl. Khim. Vol.63, No. 6, p. 1425–1428 describes a process for preparing ammonium isobutyrate by reaction of isobutyric acid with ammonia in isopentane. The influence of the ammonia pressure is investigated, albeit only with respect to the initial formation rate of ammonium isobutyrate.
Although existing processes deliver crystalline ammonium salts, the crystal size distribution is wide and the crystal size not controllable. The achievable yields are unsatisfactory.